System and method of controlling fuel delivery during positive valve overlap operation of an engine start

Abstract

An approach is provided for compensating engine fueling during starting conditions in which positive valve overlap is enabled early in the start. In one example, the valve timing is adjusted to increase positive overlap during cold starting conditions, and fuel adjustments are provided to compensate for the evaporation effects of the increased residual push-back.

1. A method for controlling fuel injection into an engine of a vehicle, the engine having at least a variable intake valve timing system, the method comprising:
 cold starting the engine with the variable valve timing system at a default position; 
 before the engine warms to a warm-up temperature, adjusting the variable intake valve timing system to generate an increase in positive valve overlap of at least one cylinder; 
 adjusting a fuel injection amount in response to said increase in positive valve overlap, where said adjusting the fuel injection amount provides a decrease in injected fuel to account for an increase in fuel evaporating from the intake valve and/or the intake port as engine temperature warms; and 
 adjusting spark timing in response to said adjusting of the variable intake valve timing system and further to maintain engine idle speed. 
 
   
   
     2. The method of  claim 1  where said adjustment of said fuel injection amount is based on an amount of positive valve overlap. 
   
   
     3. The method of  claim 2  where said adjustment continues even if the positive valve overlap remains relatively fixed after said adjustment. 
   
   
     4. The method of  claim 1  wherein the variable valve timing system is a variable cam timing system. 
   
   
     5. The method of  claim 1  wherein the warm-up temperature is a predetermined engine coolant temperature. 
   
   
     6. The method of  claim 1  wherein said positive valve overlap is increased by advancing intake valve timing. 
   
   
     7. A method for controlling fuel injection into an engine of a vehicle, the engine having a variable valve timing system, the method comprising:
 starting engine with the variable valve timing system at a default position; 
 before the engine warms to a warm-up temperature, adjusting the variable valve timing system to increase positive valve overlap of at least one cylinder; and 
 adjusting a fuel injection amount in response to said increase in positive valve overlap, said adjustment of fuel providing a decrease in injected fuel to account for an increase in fuel evaporating from the intake valve, said fuel adjustment based on an amount of pushback residual flow due to said positive valve overlap, where said residual flow is proportional to a square of an amount of overlap between intake and exhaust valves, and then later further decreasing injected fuel to account for transient fuel evaporating from the intake port as the engine temperature warms. 
 
   
   
     8. The method of  claim 7  where said adjustment of said fuel injection amount is based on an amount of positive valve overlap. 
   
   
     9. The method of  claim 8  where said adjustment continues even if the positive valve overlap remains relatively fixed after said adjustment. 
   
   
     10. The method of  claim 9  wherein the variable valve timing system is a variable cam timing system. 
   
   
     11. The method of  claim 10  wherein the warm-up temperature is a predetermined engine coolant temperature. 
   
   
     12. The method of  claim 8  wherein said fuel adjustment is based on an intake valve fuel film temperature and intake port temperature. 
   
   
     13. A method for controlling fuel injection into an engine of a vehicle, the engine having a variable valve timing system, the method comprising:
 starting engine with the variable valve timing system at a default position and with a fuel film accumulated on an intake valve of the variable valve timing system; 
 before the engine warms to a warm-up temperature, adjusting the variable valve timing system to increase positive valve overlap of at least one cylinder; 
 pushing back combusted cylinder gasses past the intake valve into an intake manifold to heat the intake valve; 
 evaporating the fuel film via said heating of the intake valve; 
 inducting at least some evaporated fuel from the film into the cylinder; and 
 adjusting a fuel injection amount in response to said increase in positive valve overlap, said adjustment of fuel providing a decrease in injected fuel to account for an increase in fuel evaporating from the intake valve as the engine temperature warms. 
 
   
   
     14. The method of  claim 13  wherein said adjusting of the fuel injection amount is based on a fuel quality and engine speed. 
   
   
     15. The method of  claim 14  wherein said adjusting of the fuel injection amount is further based on an intake valve fuel film temperature.